The hypothesis proposed to test is that reactive species of O2 are the initiators of oxidative stress-induced damage to the lenticular plasma membrane lipids and proteins in cataract. The objective is to investigate the crucial areas of the mechanism of cataract involving oxidation of proteins and peroxidation of phospholipids of plasma membranes. Exposing the lens plasma membranes to various oxidative stresses in vitro, modification of the intrinsic membrane protein MP26, will be determined using SDS polyacrylamide gel electrophoresis. After identical treatment, membrane phospholipids will be assessed by measuring the formation of aminophospholipid.malondialdehyde adduct using TLC, HPLC and spectrofluorometry. Fatty acids will be analysed by gas chromatography and HPLC. Malondialdehyde(MDA) and lipid hydroperoxides will be estimated in lens to observe their possible correlation with the loss of unsaturated fatty acids in cataracts. Polarographic and ESR spectroscopic techniques will be used to detect O2.-, OH., H2O2 and adriamycin semiquinone free radical in aqueous humor, and in lens of rabbit by addition of calf lens microsomal NADPH oxidase system in vitro. Attempts will be made to identify Schiff base conjugate formed by polymerization of aminophospholipids of lens under oxidative stress and in cataracts in the human and animal using (14C-)MDA or phosphatidyl ethanolamine. Oxidative stress-induced cross linking of membrane-SH in vitro, and in precataract and early cataract induced in rabbits by galactose will be determined by using (14C-)iodoacetamide. To assess the role of enzymic defenses in cataracts, analysis of the bioactive and inactive forms of superoxide dismutase, catalase and GSH peroxidase will be done using spectrophotometric technique and radioimmunoassay. Tests of antioxidants in the therapy of experimental cataracts will be continued. Arrest of the progression of cataract in the human at an early stage will be of immense help to the patients. The economic benefit resulting from reduction of the number of surgical procedures for cataracts also must not be underestimated.